This invention relates to the manufacture of high quality lubricating oils and, in particular, such oils based on oligomerized lower olefins. The invention is especially directed to the preparation of a high viscosity index, low pour point, low cloud point lubricating oil by the catalytic dewaxing of a waxy component-containing lubricating oil stock derived from the oligomerization of a light olefin such as propylene over a zeolite oligomerization catalyst.
Viscosity index (V.I.) is a quality parameter of considerable importance for distillate lubricating oils to be used in automotive engines and aircraft engines which are subject to wide variations in temperature. This Index indicates the rate of change of viscosity with temperature. A high viscosity index, e.g., one of at least about 85, indicates an oil that does not tend to become viscous at low temperature or become thin at high temperatures Measurement of the Saybolt Universal Viscosity of an oil at 100.degree. and 210.degree. F., and referral to correlations, provides a measure of the V.I of an oil. For purposes of the present invention, whenever V.I is referred to, the V.I. as noted in the Viscosity Index tabulations of ASTM D567 published by ASTM, or equivalent, is intended.
Recent developments in zeolite catalysts and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks, such as petroleum refinery streams rich in lower olefins, for the production of C.sub.5 + gasoline, diesel fuel, lube stocks, etc. U.S. Pat. Nos. 3,960,978; 4,021,502; 4,150,062; 4,211,640; 4,227,992; 4,456,779; and, 4,547,612 disclose the conversion of C.sub.2 -C.sub.5 olefins by catalytic oligomerization into heavier hydrocarbons over acidic zeolites catalysts.
U.S. Pat. No. 4,520,221 describes a process for producing high V.I. lubes by oligomerizing light olefins over a ZSM-5 type catalyst, the surface acidity of which has been inactivated by treatment with a suitable base material, e.g., a bulky alkylpyridine such as 2,6-di-tert-butyl pyridine.
U.S. Pat. No. 4,524,232 discloses a combination process for producing high V.I lubricating oils from light olefins employing in separate stages a small pore size zeolite catalyst, e.g., ZSM-23, and an intermediate pore size zeolite catalyst, e.g., ZSM-5.
It is known from U.S. Pat. No. 4,568,786 to catalytically oligomerize light olefin to heavier hydrocarbons in a first stage employing a medium pore acidic zeolite catalyst, e.g., H-ZSM-5, the surface of which has been rendered inactive for acidic reactions by chemisorption of a surface deactivating agent, e.g., a bulky amine such as di-tert-butyl pyridine as disclosed in U.S. Pat. No. 4,520,221, supra. The oligomerized product is then further oligomerized/interpolymerized over a second and/or different acid catalyst, e.g., boron trifluoride or an acidic zeolite such as HZSM-5 which may or not be surface treated, to provide lubricant range hydrocarbons.
In accordance with the olefin oligomerization process described in U.S. patent application Ser. No. 140,361, referred to above, a lower olefin such as propylene is oligomerized in the presence of, as catalyst, acidic ZSM-23 zeolite which has been surface-neutralized by a bulky dialkyl pyridine compound, e.g., 2,4,6-collidine (2,4,6-trimethyl pyridine). As in U.S. Pat. No. 4,568,786, supra, the resulting product is further oligomerized over an acidic oligomerization catalyst such as boron trifluoride or an acidic zeolite such as ZSM-5 to provide lube range materials.
While the lubricating oil stocks obtained by the procedures described in aforesaid U.S Pat. No. 4,568,786 possess desirably high V.I.s, e.g., at least about 85, they also contain significant quantities of waxy components which result in their having high pour points and high cloud points. Removal of at least a portion of these waxy components while retaining the high V.I.s of the oils is necessary in order to provide a lubricating oil product of acceptable low temperature characteristics.
Numerous catalytic dewaxing processes featuring the use of a zeolite hydrodewaxing catalyst have been developed to remove waxy components of a hydrocarbon oil feed by one or more chemical mechanisms such as isomerization and cracking U.S. Pat. No. 4,222,855 describes the use of ZSM-23 and ZSM-35 as hydrodewaxing catalysts for the hydrodewaxing of a lube fraction derived from petroleum, i.e., a distillate fraction boiling within the approximate range of from about 450.degree. to about 1050.degree. F. The hydrodewaxed oil is said to possess a V.I. which is considerably higher than that obtained with ZSM-5 hydrodewaxing catalyst.
Other catalytic hydrodewaxing processes are disclosed in, inter alia, U.S. Pat. No. Re. 28,398 (of original U.S. Pat. No. 3,700,585) and U.S. Pat. Nos. 3,894,938; 4,176,050; 4,181,598; 4,229,282; 4,247,388; 4,259,174; 4,376,036; 4,419,220; 4,472,266; 4,474,618; 4,501,926; 4,541,919; 4,554,065; and, 4,601,993 to mention a few.